Conventionally, medical hollow needles such as injection needles have been used in injecting drug solution, blood or the like into the body, or in collecting blood and other fluids therefrom. Such a medical hollow needle is made in a sharp shape with a beveled blade surface formed at the tip of a thin cylindrical needle tube.
There are various ways of forming the blade surface, one of which is a cutting method called “lancet cut.” The lancet cut is provided with a first inclined surface on the base side, whereas, a second inclined surface and a third inclined surface are provided on either side of the circumference toward the tip of the blade surface, inclined at the same angle in the direction opposite to each other around the central axis, while having an inclination angle larger than that of the first inclined surface.
Meanwhile, in using such a medical hollow needle, it is important to relieve the patient's pain at the time of inserting the needle, and for that purpose, a reduction in puncture resistance is required.
In order to meet such a requirement, Unexamined Japanese Patent Publication No. JP-A-10-57490 (Patent Document 1) and Unexamined Japanese Patent Publication No. JP-A-2000-262615 (Patent Document 2) propose a shape of a blade surface wherein a fourth inclined surface and fifth inclined surface are provided between the first and second inclined surfaces and between the first and third inclined surfaces, respectively. The fourth inclined surface located between the first and second inclined surfaces has a smaller rotational angle (angle in the circumferential direction) than that of the second inclined surface around the central axis relative to the first inclined surface, and at the same time, has an inclination angle against the central axis larger than the first inclined surface and smaller than the second inclined surface. Also, the fifth inclined surface located between the first and third inclined surfaces has a smaller rotational angle (angle in the circumferential direction) than that of the third inclined surface around the central axis relative to the first inclined surface, and at the same time, has an inclination angle against the central axis larger than the first inclined surface and smaller than the third inclined surface.
However, upon examination by the inventors, it became clear that the medical hollow needle in a shape of a blade surface with the first to fifth inclined surfaces described in Patent Documents 1 and 2 still has a room to improve the effect of reducing puncture resistance. Especially in the medical hollow needle with a conventional structure, as shown in FIG.3 of Patent Document 1, puncture resistance gradually increases during the needle puncture all the way from the tip end (blade edge portion) to the base end (heel portion) via the intermediate portion (ridge), and at the same time, puncture resistance gets too large at the base end as compared to the tip end and intermediate portion. For that reason, the puncture pain was continuously felt, and there was a risk of feeling a significant puncture pain at the end.